Einstein's 'Biggest Blunder' Turns Out to Be Right

Einstein's 'Biggest Blunder' Turns Out to Be Right
This Hubble image displays a pair of spiral galaxies with swirling arms. The binary galactic system is located in the constellation of Draco, the Dragon, about 350 million light-years (100 million parsecs) away. Astronomers studied galaxy pairs like this to determine the geometry of the universe, which shed light on dark energy.
(Image: © NASA, ESA, the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration, and A. Evans (University of Virginia, Charlottesville/NRAO/Stony Brook University))

What Einstein called his worstmistake, scientists are nowdepending on to help explain the universe.

In 1917, AlbertEinstein inserted a term called the cosmological constantinto his theory ofgeneral relativity to force the equations  to predict astationary universe inkeeping with physicists' thinking at the time. When it became clearthat theuniverse wasn't actually static, but was expanding instead, Einsteinabandonedthe constant, calling it the '"biggest blunder" of his life.

But lately scientists have revivedEinstein's cosmologicalconstant (denoted by the Greek capital letter lambda) to explain a mysteriousforce called dark energy that seems to be counteractinggravity ? causingthe universe to expand at an accelerating pace.

A new study confirms that thecosmological constant is thebest fit for dark energy, and offers the most precise and accurateestimate yetof its value, researchers said. The finding comes from a measurement oftheuniverse's geometry that suggests our universe is flat, rather thansphericalor curved.

Geometry of the universe

Physicists Christian Marinoni andAdeline Buzzi of theUniversite de Provence in France found a new way to test the darkenergy model that is completely independent of previousstudies. Theirmethod relies on distant observations of pairs of galaxies to measurethecurvature of space.

"The most exciting aspect of the workis that there isno external data that we plug in," Marinoni told SPACE.com, meaningthattheir findings aren't dependent on other calculations that could beflawed.

The researchers probed dark energy bystudying the geometryof the universe. The shape of space depends on what's in it ?that was oneof the revelations of Einstein's general relativity, which showed thatmass andenergy (two sides of the same coin) bend space-time with theirgravitationalforce.

Marinoni and Buzzi set out tocalculate the contents of theuniverse ? i.e. how much mass and energy, including dark energy, itholds ? bymeasuring its shape.

There were three main options for theoutcome.

Physics says the universe can eitherbe flat like a plane,spherical like a globe, or hyperbolically curved like a saddle.Previousstudies have favored the flat universe model, and this new calculationagreed.

Flat universe

The geometry of space-time candistort structures within it.The researchers studied observations of pairs of distant galaxiesorbiting eachother for evidence of this distortion, and used the magnitude of thedistortionas a way to trace the shape of space-time.

To discover how much the galaxypairs' shapes were beingdistorted, the researchers measured how much each galaxy's light wasred-shifted ? that is, budged toward the red end of the visual spectrumby aprocess called the Doppler shift, which affects moving light or soundwaves.

The redshift measurements offered away to plot theorientation and position of the orbiting pairs of galaxies. The resultof thesecalculations pointed toward a flat universe.

Marinoni and Buzzi detail theirfindings in the Nov. 25issue of the journal Nature.

Understanding dark energy

By providing more evidence that theuniverse is flat, the findingsbolster the cosmologicalconstant model for dark energy over competing theories suchas the ideathat the general relativity equations for gravity are flawed.

"We have at this moment the mostprecise measurementsof lambda that a single technique can give," Marinoni said. "Our datapoints towards a cosmological constant because the value of lambda wemeasureis close to minus one, which is the value predicted if dark energy isthecosmological constant."

Unfortunately, knowing that thecosmological constant is thebest mathematical explanation for how dark energy is stretching out ouruniverse doesn't help much in understanding why it exists at all.

"Many cosmologists regard determiningthe nature ofdark energy and dark matter as the most important scientific questionof thedecade," wrote Alan Heavens of Scotland's University of Edinburgh in anaccompanying essay in the same issue of Nature. "Our picture of theuniverse involves putting together a number of pieces of evidence, soit isappealing to hear of Marinoni and Buzzi?s novel technique for testingthecosmological model, not least because it provides a very direct andsimplemeasurement of the geometry of the universe."

You can follow SPACE.comsenior writer Clara Moskowitz onTwitter @ClaraMoskowitz.

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